Today a friend told me something disturbing... Bananas are radioactive. Found it hard to believe. But when googeling a bit it seems true. Only thing on the internet that is not consistent is how many would it take to kill a human? And is it possible to calculate how many exactly?
The radioactivity from bananas comes from Potassium and it's not possible to die from eating a particular dose. It may actually be possible to die from being in contact with bananas over a prolonged period of time, but you would need to spend decades around thousands of them.
Your body already contains a certain amount of potassium and when you eat something else that contains potassium you are topping up your reserve with any excess discarded by your kidneys. The period that you are in contact with this additional radiation is only going to be a few hours before it is broken down.
It's not just bananas that contain radioactive metals. Potassium can be found in lots of other plants/ foods including potatoes and seeds.
I noted the answer from Jeff that you would need to eat forty six million and whereas that may be enough contact radiation to kill (I haven't personally worked it out), it's not possible to eat that many bananas so you still could not die from eating them.
There are plenty of other sources of radiation found in food. There is a source of radium found in drinking water which varies depending on the source and this is also found in peanut butter.
Wikipedia's article on the Sievert, a unit used to measure radiation, tells us a banana's output measures about 0.098 μSv. The lowest fatal dose listed is 4.5 Sv. So we know the radiation from forty-six million bananas would be enough to kill.
Annual world production of bananas is around 18 million tonnes, and at 125g per banana, that's enough to kill 3000 people every year if all the bananas are produced on the same day instead of throughout the year and if the bananas are arranged in spheres around the people to maximize radiation exposure. The same mass could probably be used to crush or suffocate a larger number of people.